dineutron

Dineutron is a term used in nuclear physics to describe a system containing two neutrons. In free space, two neutrons do not form a bound state; the neutron–neutron interaction, while attractive in the 1S0 channel, is not strong enough to bind the pair against their kinetic energy. The S-wave interaction is characterized by a large negative scattering length, indicating a virtual state near threshold rather than a true bound di-neutron.

In nuclear structure, the concept of a dineutron often refers to a spatial correlation between two neutrons within a nucleus, especially in neutron-rich or halo systems. In such cases, two neutrons can form a correlated pair around a core, influencing the structure and decay patterns of the nucleus even without a bound di-neutron in vacuum. Dineutron correlations are discussed in the study of light exotic nuclei such as halo systems, where the two neutrons may cluster temporarily or affect reaction dynamics and two-neutron emission processes.

Experimentally, no bound dineutron has been observed in isolation. Evidence related to dineutron concepts typically comes from indirect measurements of neutron–neutron correlations, decay products of nuclear reactions, or theoretical models that describe two-neutron emission as a correlated pair rather than as two independent neutrons. The idea of a dineutron resonance or near-threshold states has been explored in various theoretical frameworks, but a stable two-neutron bound state in free space remains unsupported by experimental data.

See also: neutron–neutron interaction, halo nucleus, Borromean nucleus, two-neutron emission.